Many commercially available curable liquid rubber polymer compositions exhibit a wide range of useful mechanical, physical and electrical bulk properties. Additionally these compositions can be provided at relatively low cost. There is a continuing need for materials with such useful properties in diverse applications which also require superior surface properties such as exceptional weatherability, superior fire resistance, enhanced solvent resistance, durable hydrophobicity and good release properties. Such superior surface properties are generally lacking in low-cost, curable liquid rubber compositions but are typically exhibited by more-costly halogen-containing polymers, especially fluoropolymers.
For many years technologists have tried to develop methods of bringing together the useful properties of inexpensive fluorine-free polymers with the surface properties of fluoropolymers. One technique involves laminating a fluoropolymer layer to a non-fluoropolymer layer to form a multilayer composite. Unfortunately and ironically, the highly prized surface properties which make fluoropolymers poorly adherent to dissimilar materials also causes the desirable laminar composites of fluoropolymers and nonfluoropolymers to exhibit low interfacial peel strength and a tendency to delaminate.
U.S. Pat. No. 5,916,659 of Koerber et al. discloses composites of fluoropolymers with non-fluoropolymers and a method of forming such composites. The disclosure calls for laminating onto opposite faces of a non-woven, fibrous binder, a layer of fluoropolymer and a layer of non-fluoropolymer such that a portion of the cross-sectional thickness of the non-woven binder is embedded into the fluoropolymer layer and a part or all of the remaining portion of the cross-sectional thickness of the binder is embedded into the non-fluoropolymer layer.
The fluoropolymer component typically is the overwhelmingly highest unit cost material of the composite. Also, the properties provided by the fluoropolymer can usually be adequately imparted to the product by an extremely thin coating of fluoropolymer on the surface of the composite. Therefore, there is a forceful motivation to use as little fluoropolymer in as thin a layer as possible.
Generally conventional composites and methods of fluoropolymer and non-fluoropolymer layers utilize fluoropolymer layers formed from thick films of greater than 51 μm (2 mils) thickness. Film of less thickness is usually too weak to be self-supporting or to withstand normal manipulation experienced during the fabrication of the composite. Thin film can be produced by carefully skiving sections from a fluoropolymer billet, however this is a very difficult procedure to carry out successfully. Naturally, these thin films are extremely delicate and must be handled with extreme care to maintain their structural integrity.
Consequently, there is a need for a laminar composite of non-fluoropolymer bonded strongly to a layer of fluoropolymer of uniform thickness of 50 μm or less. It is also desirable to have a method of making such a laminar composite in a simple, highly productive and cost effective manner. Composites of this structure would find potential use in diverse applications such as waste pond liners, mold release liners, molded gas tanks, conveyor belts, grill sheets and belts, insulation covering for aerospace application products, and exterior and interior architectural components, for example, roofs and walls.